The number of children diagnosed with attention deficit hyperactivity disorder (ADHD) has reached more than 10 percent, a significant increase during the past 20 years, according to a study released Friday.

The rise was most pronounced in minority groups, suggesting that better access to health insurance and mental health treatment through the Affordable Care Act might have played some role in the increase. The rate of diagnosis during that time period doubled in girls, although it was still much lower than in boys.

But the researchers say they found no evidence confirming frequent complaints that the condition is overdiagnosed or misdiagnosed.

The U.S. has significantly more instances of ADHD than other developed countries, which researchers said has led some to think Americans are overdiagnosing children. Dr. Wei Bao, the lead author of the study, said in an interview that a review of studies around the world doesn’t support that.

”I don’t think overdiagnosis is the main issue,” he said.

Nonetheless, those doubts persist. Dr. Stephen Hinshaw, who co-authored a 2014 book called “The ADHD Explosion: Myths, Medication, Money, and Today’s Push for Performance,” compared ADHD to depression. He said in an interview that neither condition has unequivocal biological markers, so it makes it hard to determine if a patient truly has the condition without lengthy psychological evaluations. Symptoms of ADHD can include inattention, fidgety behavior and impulsivity.

“It’s probably not a true epidemic of ADHD,” said Hinshaw, a professor of psychology at the University of California-Berkeley and a professor of psychiatry at UC-San Francisco. “It might be an epidemic of diagnosing it.”

In interpreting their results, however, the study’s authors tied the higher numbers to better understanding of the condition by doctors and the public, new standards for diagnosis and an increase in access to health insurance through the ACA.

Because of the ACA, “some low-income families have improved access to services and referrals,” said Bao, an assistant professor of epidemiology at the University of Iowa College of Public Health.

The study, published in JAMA Pediatrics, used data from the National Health Interview Survey, an annual federal survey of about 35,000 households. It found a steady increase in diagnoses among children from about 6 percent of children between 1997 and 1998 to more than 10 percent between 2015 and 2016.

Advances in medical technology also may have contributed to the increase, according to the research. Twenty years ago, preterm or low-weight babies had a harder time surviving. Those factors increase the risk of being diagnosed with ADHD.

The study also suggests that fewer stigmas about mental health care in minority communities may also lead to more people receiving an ADHD diagnosis.

In the late 1990s, 7.2 percent of non-Hispanic white children, 4.7 percent of non-Hispanic black children and 3.6 of Hispanic children were diagnosed with ADHD, according to the study.

By 2016, it was 12 percent of white kids, 12.8 percent of blacks and 6.1 percent of Hispanics.

Over the past several decades, Hinshaw said, there’s been an expanded view of who can develop ADHD. It’s no longer viewed as a disease that affects only white middle-class boys, as eating disorders are no longer seen as afflicting only white middle-class girls.

Still, he cautioned against overdiagnosing ADHD in communities where behavioral issues could be the result of social or environmental factors such as overcrowded classrooms.

The study found rates of ADHD among girls rose from 3 to more than 6 percent over the study period. It said that was partly a result of a change in how the condition is classified. For years, ADHD pertained to children who were hyperactive. But in recent years, the American Psychiatric Association added to its guide of mental health conditions that diagnosis should also include some children who are inattentive, Bao said. That raised the number of girls, he explained, because it seems they are more likely to be in that second subtype.

“If we compare these two, you can easily imagine people will easily recognize hyperactivity,” he said.

That rang true for Ruth Hay, a 25-year-old student and cook from New York who now lives in Jerusalem. She was diagnosed with what was then called ADD the summer between second and third grade.

Hay said her hyperactive tendencies aren’t as “loud” as some people’s. She’s less likely to bounce around a room than she is to bounce in her chair, she said.

Yet despite her early diagnosis, Hay said, no one ever told her about other symptoms. For example, she said, she suffers from executive dysfunction, which leaves her feeling unable to accomplish tasks, no matter how much she wanted to or tried.

“I grew up being called lazy in periods of time when I wasn’t,” Hay said. “If you look at a list of all the various ADHD symptoms, I have all of them to one degree or another, but the only ones ever discussed with me was you might be less focused and more fidgety.”

“I don’t know how my brain would be if I didn’t have it,” she added. “I don’t know if I’d still be me, but all it has been for me is a disability.”

KHN’s coverage of children’s health care issues is supported in part by the Heising-Simons Foundation.

This story was produced by Kaiser Health News, an editorially independent program of the Kaiser Family Foundation.

Kaiser Health News (KHN) is a nonprofit news service committed to in-depth coverage of health care policy and politics. And we report on how the health care system — hospitals, doctors, nurses, insurers, governments, consumers — works.